A Model Mechanism for the Enzymatic Synthesis of Lupin Alkaloids

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Abstract
A crude enzyme preparation obtained from cell suspension cultures of L. polyphyllus catalyzed the pyruvate-dependent conversion of cadaverine into the tetracyclic lupin alkaloids. As the 1st reaction product, 17-oxosparteine could be identified by GLC and mass spectroscopy. In some experiments sparteine was also found. A participation of diamine oxidase could be ruled out. The cadaverine-pyruvate transaminating enzyme system (17-oxosparteine synthase) catalyzed the formation of 17-oxosparteine from 3 cadaverine units without releasing free intermediates. These results are inconsistent with the hypothetical mechanism thus far formulated for the lupin alkaloid biosynthesis. A new enzymatic model mechanism is proposed regarding both the results of the enzymatic experiments and those of the in vivo tracer studies.